Small amounts of Al are added to molten zinc during continuous galvanizing of steel to control the reaction between the iron of the strip and the zinc in the bath. The aluminum retards the formation of brittle Fe/Zn intermetallic phases on the surface of the strip.
Control of Al in Zn is also important to Zn producers who supply pre-alloyed Al-Zn ingots to the steel galvanizing industry.
Al is added to Zn in specific amounts to produce some Zn/Al casting alloys. The amount of Al will control the properties of the alloy.
In all cases, to determine the Al level, samples are taken from a molten bath, solidified and subsequently analyzed elsewhere by existing analytical techniques. This is a slow process and can cause delays if the analyses are used for process control. Also, the precision of some of the analytical techniques is barely comparable to the analytical accuracy required, especially in the case of galvanizing. In addition, because analytical samples are not always homogenous in terms of the Al concentration, misleading results are often encountered. Local variations in the Al concentration within the analytical sample happen frequently due to the presence of Al-bearing second phase particles and to aluminum segregation during solidification.